The present invention relates to surgical support apparatus, and more particularly, to a component of an improved blood oxygenator used to maintain a patient's blood at a predetermined temperature while replacing carbon dioxide in the blood with oxygen.
Blood oxygenators are well known in the medical field. Typically they are disposable components of so-called "heart-lung machines." These machines mechanically pump a patient's blood and oxygenate the blood during major surgery such as a heart bypass operation. A typical commercially available blood oxygenator includes a heat exchanger and a membrane-type oxygenator. The patient's blood is continuously pumped through the heat exchanger. A suitable heat transfer fluid such as water is also pumped through the heat exchanger separated from the blood but in heat transfer relationship therewith. The water is either heated or cooled externally of the blood oxygenator to maintain the patient's blood at a predetermined desired temperature. The membrane oxygenator comprises a so-called "bundle" of thousands of tiny hollow fibers made of a special polymer material having microscopic pores. Blood exiting the heat exchanger flows around the outside surfaces of these fibers. At the same time an oxygen-rich gas mixture, sometimes including anesthetic agents, flows through the hollow fibers. Due to the relatively high concentration of carbon dioxide in the blood arriving from the patient, carbon dioxide from the blood diffuses through the microscopic pores in the fibers and into the gas mixture. Due to the relatively low concentration of oxygen in the blood arriving from the patient, oxygen from the gas mixture diffuses through the microscopic pores in the fibers into the blood. The oxygen content of the blood is raised, and its carbon dioxide content is reduced. The blood is also heated or cooled before being returned to the patient.
A blood oxygenator must have a sufficient volumetric flow rate to allow proper temperature control and oxygenation. However, blood is typically in short supply and is very expensive. Therefore, it is desirable to minimize the volume of blood contained within the oxygenator, preferably to less than five hundred cubic centimeters. The cells and platelets in human blood are delicate and can be traumatized if subjected to excessive shear forces. Therefore, the blood flow velocity inside a blood oxygenator must not be excessive. In addition, the configuration and geometry of the inlet nozzle, manifolds and outlet nozzle of the blood flow path for a given blood flow rate must not create re-circulations (eddies) or stagnant areas that can lead to clotting.
After the blood has flowed around the fibers of the membrane oxygenator, it must be collected and routed outside the blood oxygenator in a uniform and efficient manner. This requires an optimally configured outlet manifold that couples to an outlet nozzle sized for connection to the standard flexible tubing that conveys the blood back to the patient.